There is known an electronic apparatus which includes: a backplane provided with plural connectors; and plural electronic units respectively connected to the connectors. The electronic unit has a unit board on which electronic parts are mounted. The unit board and the backplane are electrically connected to each other, whereby signals and electricity are supplied to the electronic parts mounted on the unit board. For example, there is known a technique of connecting electronic units each having a different shape factor to the backplane efficiently within a given space (See Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2004-503890).
Since the plural electronic units are connected to the backplane, so that the great ratio of the backplane is occupied in the whole electronic apparatus. Thus, even if the electronic unit is able to be connected efficiently in the limited space, the whole electronic apparatus might be large when the backplane is large. The upsizing of an electronic apparatus causes the degradation of the cooling efficiency, the increase in the production cost with the upsizing of the housing or the cooling fan, and the increase in its weight.